Chronic cough is a cough that lasts for more than eight weeks and is associated with significant adverse social, psychosocial and physical effects on quality of life. It is estimated that, in the United States alone, more than 27 million patients suffer from chronic cough. While an underlying etiology such as gastro-oesophageal reflux, asthma, or allergic rhinitis may contribute to cough in some of these patients, an underlying condition cannot be identified in 10%-40% of chronic cough patients (unexplained chronic cough). A portion of patients with an underlying condition as well as the large majority of unexplained chronic cough patients are not well controlled by current therapies.